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Discussion Starter · #1 ·
I just bought a Triumph twin motor (TR6SR DU19456) and a 64 Triumph frame (TR6R DU9623) with a bolt on hardtail.




The motor parts are scattered all over, but it has two cranks and a freshly rebuilt head.





I've got a few questions about the motor.

#1: In the pictures, one crank looks a lot thicker than the other. Is there a difference in 650 cranks? Since this is an SR (Street Racer) motor, was the crank lighter?

#2: Will parts interchange between the TR6SR and a 1971 T-120 motor? I have a T-120 motor that was run without oil, so the bearings and rods are probably toasted, and the pistons are DEFINITELY toasted. I want to mix and match to keep it cheep.

#3: The cams and timing wheels are a little rusty. What's the best way to clean them up? Is it safe to run the cams with just a scuffing, or do they need to be reground/replaced?

Thanks for helping the Triumph-impaired.

-JEB
 

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#1: In the pictures, one crank looks a lot thicker than the other. Is there a difference in 650 cranks? Since this is an SR (Street Racer) motor, was the crank lighter? What part of the crank is thicker? The whole thing or just the end? I have seen people machine down the end of a newer 650 crank to use for lack of a pre-68 crank.

#2: Will parts interchange between the TR6SR and a 1971 T-120 motor? I have a T-120 motor that was run without oil, so the bearings and rods are probably toasted, and the pistons are DEFINITELY toasted. I want to mix and match to keep it cheep. I am almost positive the parts won't interchange. I definitely know you can't use any of the head bolts.

#3: The cams and timing wheels are a little rusty. What's the best way to clean them up? Is it safe to run the cams with just a scuffing, or do they need to be reground/replaced? Get new ones. You can find them cheap on Ebay...i never trust parts that are rusty as shit.
 

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First I have a 1965 TR6SR that I built for my wife. Iv'e been building Harleys for 30+ years but had to learn Limey for this build. A good manual (preferably a Factory one, but a Clymer will do) will be worth it's weight in gold. Iv'e never heard the SR designation refered to as Street Racer but more as an export and equipment identifier as my Factory Manual 1963-1970 makes No mention of the letter "S" in dealing with the engines or bike. Anyway most all Unit construction 650 parts will interchange. The T120 is rated @47hp while the TR6 is rated @43 most likely due to the 120's dual carb head flowing better at top end. The crank pictured has been cut down (lightened) for drag racing and the other is stock. As for cleaning parts, light rust that wire brushes off and leaves no pits or marks is ok anything else in a motor is just asking for problems.
 

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G'day,here some thoughts,
The designation SR given to triumphs means "Sports Road" not as cool as street racer but hey ,Edward Turner the Triumph head honcho was a conservative kinda guy.
Yeah triumphs did make three flywheels to suit 650s,the big (heavier) one was from 63 upto 66 then a lighter by 2 lbs from 66-71 .from mid 71 the crank went metric for the main bearings so that crank wont fit earlier cases unless you do some work and it got its own flywheel. An earlier reply suggests that your smaller (lighter )crank has been machined and I recon they is right, but find your local triumph guru and double check.
A lot of your 71 parts will fit the 65 SR ,you can even drop the 71 head & barrels onto the 65 ,really the crank is the major non swapable part.The timing gears from the 71 should fit the 65.Oh yeah the heavier flywheel is good for a street bike,so if youre not into stoplight racing I'd go with that (I did on my 67 bonnie with a 68 motor).
Out of interest,what motor are you planing on rebuilding?
Cheers
 

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JEB said:
#2: Will parts interchange between the TR6SR and a 1971 T-120 motor? I have a T-120 motor that was run without oil, so the bearings and rods are probably toasted, and the pistons are DEFINITELY toasted. I want to mix and match to keep it cheep.

#3: The cams and timing wheels are a little rusty. What's the best way to clean them up? Is it safe to run the cams with just a scuffing, or do they need to be reground/replaced?

Thanks for helping the Triumph-impaired.

-JEB
#2 - Most parts will indeed. It is true that the only major differences between the two are the crank and dual carb head.

#3 - I'd get new. Even sandblasting them you're not going to have smooth surfaces (plus you'll be adding play), and the frictions build up will cause the gears to self destruct.
 

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Discussion Starter · #6 ·
Thanks for the help, guys. Heh heh, the Street Racer name was wishful thinking on my part, I should have put a question mark at the end. I called my local Triumph shop (Southwest Choppers) today and they also called it a "Sports Road" so that must be the right name.

I'm getting the parts on Sunday or Monday (thanks to JimC over on the HAMB for delivering) so I'll take more pics and ask more questions when I get my hands on the pieces.Right now it looks like I'll rebuild the TR6SR motor, unless there's a big problem with the crank or the cases.

More later,
-JB
 

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Heres a scaned picture of an article on turning down Triumph flywheels. I bought an old reprint of a Triumph Speed Secrets (Tuning the B range engine) on ebay along with a lot of other people I think.. It seems to be from the very late 60's or early 70's. Some good info although mostly outdated. Some realy cool pictures of old Triumph race bikes. Sports Road.. Iv'e asked a lot of people and nobody knew, makes sence. It must have been a US marketing thing as the SR designation dosen't appear in my factory service book anywhere.
 

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Discussion Starter · #8 ·
I got all the parts last week and started sorting the motor. It's definitely a steal. I got a rebuilt head, freshly bored cylinders, rebuilt AMAL monobloc, clean cases, good 4-speed tranny, fresh rods and new 20 over pistons. The crank was rebuilt, clean as a whistle, but I'm gonna pull the sludge trap myself, just to be sure. Scott over at Southwest Choppers is helping out. I'm gonna have to replace all the bearings, rod shell bearings, gaskets, seals and rings and that's it!

Should have enough parts left over to do another motor after this one is built. Jason Mcelroy has a VERY detailed website showing his rebuild http://www.jasonmcelroy.com/mahoney_1.html , and it's helping me wrap my head around it all.
 

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JEB said:
I got all the parts last week and started sorting the motor. It's definitely a steal. I got a rebuilt head, freshly bored cylinders, rebuilt AMAL monobloc, clean cases, good 4-speed tranny, fresh rods and new 20 over pistons. The crank was rebuilt, clean as a whistle, but I'm gonna pull the sludge trap myself, just to be sure.
That's great news man. Glad to hear that you got a bundle of good stuff. Except for wear parts and a couple of bits, it sounds like you're ready to build. Good idea on double checking that sludge trap.

I think I've posted about this elsewhere but get yourself a Haynes manual, a factory parts list for your appropriate year, and if you can find/afford one an out-of-print book by David Gaylin called Triumph Motorcycle Restoration Guide. The David Gaylin book is expensive but it's really helpful if you're going to work on Triumphs a lot.
 

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Discussion Starter · #10 ·
BigDdy31 said:
That's great news man. Glad to hear that you got a bundle of good stuff. Except for wear parts and a couple of bits, it sounds like you're ready to build. Good idea on double checking that sludge trap.

I think I've posted about this elsewhere but get yourself a Haynes manual, a factory parts list for your appropriate year, and if you can find/afford one an out-of-print book by David Gaylin called Triumph Motorcycle Restoration Guide. The David Gaylin book is expensive but it's really helpful if you're going to work on Triumphs a lot.
Oh yeah, I also got a Haynes manual in the deal. I'll look around for the David Gaylin book. What about Whitworth tools? I'm gonna need some "spanners", any advice on a good starter set? What do I need and where to get them?
 
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